This invention relates to anti-skid braking systems for vehicles.
Systems are already well known for detecting wheel deceleration during braking and releasing the brake on a wheel which is decelerating too rapidly. Brake release is achieved by closing a valve which is included in the connection between an hydraulic master cylinder and a slave cylinder and simultaneously actuating a de-booster device which increases the volume of the part of the connection between the valve and the slave cylinder, operation of the system taking place under the influence of an anti-skid controller.
With such a system a problem can arise at the time of brake re-application after recovery of the wheel from its slip, particularly when the wheel is travelling across a surface of which the coefficient of friction is increasing as the wheel travels, e.g. when passing from a wet road area to a dry one. When re-application is instructed by the anti-skid controller, the de-booster is deactuated and the valve is re-opened. At this time, the master cylinder pressure is very significantly higher than the slave cylinder pressure and the sudden fluid inrush which occurs when the valve opens can cause the wheel deceleration to be raised above the threshold, thereby triggering another anti-skid release cycle.